Effects of cytotoxic T lymphocyte antigen 4 (CTLA4) signaling and locally applied steroid on retinal dysfunction by recoverin, cancer-associated retinopathy antigen.

PURPOSE: To assess the cytotoxic T lymphocyte antigen 4 (CTLA4) pathway in the recoverin peptide (R64; AYAQHVFRSF) mouse model of cancer-associated retinopathy (CAR) and to assess the protective effects of subconjunctival triamcinalone injections in this model.
METHODS: To study the role of the CTLA4 pathway on the R64-induced mouse model of CAR, BALB/c mice were immunized with R64. The mice were further intraperitoneally treated with anti-CTLA4 antibody to get stronger immunoreaction. The development of CAR was evaluated by electroretinogram (ERG) examinations 21 days after treatment. A cytotoxicity assay was employed to detect induction of R64-specific cytotoxic T lymphocytes (CTLs). Immunoblotting to assess the development of anti-recoverin antibody and a T cell proliferation assay to determine the activity of lymphocytes against R64 were examined in two experimental groups, anti-CTLA4 antibody treated and untreated mice.To study the protective effect of subconjunctival triamcinalone in this model, mice immunized with R64 peptide and anti-CTLA4 antibody were either treated with 50 mg/kg/body weight of triamcinalone or phosphate buffered saline (PBS). These mice were assayed using ERG and histological examination 35 days after the first R64 immunization.
RESULTS: When mice were challenged with R64 peptide and anti-CTLA4 antibody, R64 peptide-specific CTLs were induced and decreased b-wave amplitudes were observed in ERG. Conversely, no CAR symptoms were detected in mice not treated with anti-CTLA4 antibody. Anti-CTLA4 antibody treatment did not give any significant differences in T cell proliferation and humoral reaction against recoverin. Subconjunctival triamcinalone treated mice show a trend toward improved survival of outer nuclear layer cell bodies, but did not show significant improvement of ERG amplitudes compared to the untreated mice.
CONCLUSIONS: Inhibition of the CTLA4 pathway is essential for the development of recoverin-induced murine CAR, suggesting that strengthening negative T cell signaling through CTLA4 may lessen the retinal degenerations in CAR-affected subjects. The positive effects of attenuation of the CTLA4 pathway must be weighed against a potential negative effect on survival since this pathway may also provide natural immunotherapy against the underlying malignancy. Subconjunctival injections of triamcinalone may have beneficial effects on the integrity of the outer nuclear layer (ONL) of the retina in the CAR model, although there was no significant effect on the ERG recordings.